1. Field of the Invention
In general, the present invention relates to systems and methods that use a hydrogen separator to separate molecular hydrogen from a volume of a mixed gas for use in powering a fuel cell. More particularly, the present invention is related to systems and methods that process the raffinate output of a hydrogen separator.
2. Prior Art Description
In industry, there are many applications for the use of ultra pure molecular hydrogen. For instance, there are many fuel cells that operate using hydrogen. The hydrogen, however, must be ultra pure. Any molecules of carbon dioxide, carbon monoxide or other contaminant gases that are received by the fuel cell causes damage to the fuel cell and decreases both the efficiency and the functional life of the fuel cell.
Commonly, purified hydrogen for use by a fuel cell is generated using a two stage process. In the first stage, hydrogen gas is separated from a source gas. For example, hydrogen can be separated from a hydrocarbon gas. However, in many common processes that produce hydrogen, the hydrogen gas produced is not pure. Rather, when hydrogen is produced, the resultant gas is often contaminated with hydrocarbons and/or other contaminants. It is for this reason that a second processing stage is used.
In the second processing stage, the separated hydrogen gas is then purified to remove lingering contaminants. In the art, ultra pure hydrogen is commonly considered to be hydrogen having purity levels of at least 99.999%. In the prior art, one of the most common ways to purify contaminated hydrogen gas is to pass the gas through a hydrogen separator. A hydrogen separator has a membrane made of a hydrogen permeable material, such as palladium or a palladium alloy. As the contaminated hydrogen gas is exposed to the membrane, atomic hydrogen permeates through the membrane, thereby separating from the contaminants. At the surface of the membrane, molecular hydrogen disassociates into atomic hydrogen. The membrane absorbs the atomic hydrogen. The atomic hydrogen permeates through the membrane from a high pressure side of the membrane to a low pressure side of the membrane. Once at the low pressure side of the membrane, the atomic hydrogen recombines to form molecular hydrogen.
The gases that do not pass through the membrane are commonly considered waste and are vented. However, in certain fuel cell systems, the waste raffinate gases created by a hydrogen separator contain both heat and water that can be reclaimed. The problem is that the raffinate gases may also contain sulfur compounds that must be separated from any water that is reclaimed.
A need therefore exists for a way to remove sulfur compounds from the raffinate gases of a hydrogen separator so that the heat and water contained in those raffinate gases can be reclaimed. This need is met by the present invention as described and claimed below.